1. Field of the Invention
The present invention relates to a scanning apparatus for use in, for example, electronic copiers, which is designed to optically scan an original.
2. Description of the Related Art
Of the electronic copiers hitherto known, some contain a scanning apparatus designed to optically scan an original, while moving relative to the original. To be more specific, the scanning apparatus applies light to the original. The light reflected from the original is guided to a photosensitive drum, forming thereon an image which is identical to the image formed on the original.
For example, the scanning apparatus disclosed in Jpn. Pat. Appln. KOKOKU Publication No. 5-2214 has a carriage base which can be moved by a carriage motor in a scanning direction, i.e., the direction in which the apparatus scans an original. Mounted on the carriage base are an exposure lamp, a reflector, a mirror, and a cover. The exposure lamp emits light. The reflector reflects the light to the original. The mirror receives the light reflected from the original and applies it in a predetermined direction. The exposure lamp, the reflector, the mirror, and the cover constitute an exposure/scanning unit.
A pair of sliding members are attached to the bottom of the carriage base. They extend parallel to the scanning direction and are spaced apart from each other in the direction at right angles to the scanning direction. The sliding members are placed in sliding contact with a pair of guide rails. Hence, the carriage base can move, slinging on the guide rails.
The distance between the sliding members is less than the width of the carriage base. The center of gravity of the exposure unit mounted on the carriage base is likely to be located outside the space between the sliding members. Inevitably, the exposure unit is unstable as it is moved in the scanning direction. The unit may jump and shake as it is accelerated or decelerated. As a consequence, there will be formed a blurred image on the photosensitive drum, and the unit will make noise when moved in the scanning direction.
The exposure unit can be made stable while being moved in the scanning direction, only if the width of the carriage base is increased so that the sliding members may be spaced apart for a longer distance. Then, the carriage base can have its center of gravity located in the space between the sliding members. However, the broader the carriage base, the heavier it is. The load torque of the carriage motor increases in proportion to the weight of the carriage base, rendering it more possible that the motor may malfunction. It is therefore difficult to use a broader carriage base.